#philly #weather #pawx #philadelphia #phillywx #snowstorm
Was the snow storm really a ‘Blizzard” as defined by NOAA? A review of the NWS KPHL website shows only about 1 hour visibility of 0.25 mile or less, instead of the defined 3 hours. Wind gusts were not sustained at over 35 mph for 3 hours either. So, while the storm will likely be remembered as the “Blizzard of 2026”, it really wasn’t. (Areas near the shore likely qualified for the blizzard designation.)
A few things about the models. Timing the transition from rain to snow was very good. Perfect snow total predictions are never achieved, just as rainfall is never exactly as forecast.
It should be remembered that the GFS model did much better than the ECMWF with this storm, for days in advance. The ECMWF-AI did much better than the regular ECMWF. The Canadian models were under-performers as was the German ICON model. The new RRFS, waiting to be released, was very disappointing, especially with its forecast at 60 hours and 84 hours in advance. However, the 24 hour snow forecast was very good.
The old NAM did much better than the RRFS at 60 to 84 hours. The NBM median was pretty good, maybe a tad high in some areas.
Snow Tapering Off
Posted Monday 02/23/26 @ 9:51 AM — The storm is well to our east and the vertical motion (Omega) near and west of Philadelphia has turned to a downward motion. Snow continues to rotate around the low into the city from the northeast along the 700 mb (~10,000 ft) wind direction but as it meets downward vertical motion, it should taper off. Additional scatted snow showers still possible into early afternoon near the city.
Additional snowfall from the 13z NBM (8AM) run is minimal west of the city.
I’ll do a wrap up and forecast review later today.
Additional Snowfall
Posted Sunday 02/22/26 @ 10:27 PM — Despite the afternoon’s models suggesting a more eastward track, the latest model blend (NBM) shows significant additional snow from 8 PM through 4 PM. (In the city, snow tapers to just snow showers/flurries by 12 PM)
If this holds, the NBM mean snowfall (appeared too high) did the best at predicting this storm’s snowfall.
Updates Monday morning.
Storm Update
Posted Sunday 02/22/26 @ 5:58 PM — Folks, I violated my own cardinal rule- “never look at the new model runs when the storm is in progress”.
The reason: it always changes and you never know if it’s a dramatic change in the forecast or if it’s a model “spin-up” error. Put another way, the latest models are not often not the best once a storm is in progress. I mentioned this aspect this this morning.
So, I looked at the latest GFS and RRFS models (18z) , and I shouldn’t have been surprised that the predicted snow amounts are significantly less. Is this a real change? Or a spin-up error?
(Models literally re-create the atmosphere mathematically; they often have a multi-hour “spin-up” time for the model to come close to matching the atmosphere.)
Anyhow, here’s the latest RRFS, which has cut back the snow totals. (The GFS has gone even lower to only 6 inches in Philly.)
Snowstorm Update
Posted Sunday 02/22/26 @ 3:51 PM — As forecast, it started snowing between 3 and 4 PM in many areas. Near ground temperatures are still above freezing, according to the RTMA, (however the hourly RAP model indicates that temperatures about 800 feet above ground are at or below 32º) —
The 1 PM (18z) HRRR has chimed in with its snow forecast and it remains in the range I’ve been supporting—
Last but not least, the latest NBM run with updated precipitation (19z) is available and the median snowfall has increased from the last run. I’m still placing bets on the median snowfall. (hard to believe, but the mean is even greater)
Sunday Storm Update
Posted Sunday 02/22/26 @ 11:50 AM — The latest RRFS finally caught up with the rest of the models regarding snow accumulation—
Additionally, a newer run of the NBM (13z) showed somewhat higher median snow totals than what was posted earlier.
No real change in the timeline. Snow starts accumulating between 2 and 4 PM RRFS model—
Winds
Sunday Storm Update
Posted Sunday 02/22/26 @ 8:28 AM — The models show little change from last night, perhaps a bit higher snow totals. The ECMWF’s low pressure position finally caught up with the position the GFS was forecasting all week. (Who says the ECMWF is the Mercedes and our GFS is a Chevy ?) Here’s the current position of the low—
Time line is similar to that posted yesterday. Current rain or rain/snow mix changes more to snow around noon or 1 PM. Then all snow by 3-4 PM in the city and westward. Accumulations start about 4 PM or so. The storm tapers and ends around 11 AM- noon Monday. Some additional snow showers possible in the afternoon.
Here are some of the latest snow accumulation totals—
NAM built-in algorithm— (Generally too low)
The NBM median and mean (implying higher certainty) are reasonably close together and I’m going with the median snow accumulation below (the mean values are even higher!) —
The GFS built-in snow depth values are about 1 inch less than the the NAM shown above.
Here’s my “experimental” values calculated on GFS data of precipitation and temperatures at 4 levels and water-snow ratio; they are similar to the NBM median—
At this point, with consistent model forecasts, I’m not inclined to change my forecast. Any newer models today may not have the proper ‘spin-up’ time to capture the atmosphere.
I know my snow forecast with this storm is different and higher than forecast by the TV forecasts and the NWS.
Interestingly, the RRFS and REFS (expected to become operational soon) are in the 8-10″ range for the city. I’m somewhat disappointed that both models are slow to pickup this storm at 60 and 84 hours and are perhaps forecasting snow totals. that are too low, especially the RRFS.
I guess we’ll see what happens.
I’ll update during the day as needed.
Final Storm Thoughts for this Evening
Updated Saturday 02/21/26 @ 11:40 PM —Based on tonight’s models, I’m thinking the TV forecasts of 8-12 inches of snow near the city may be too low. I’m staying with the NBM median and even my experimental forecast below.
Posted Saturday 02/21/26 @ 8:51 PM — The snow totals forecast I heard on TV this evening was 8-12 inches. A reasonable number, and depending on how much precipitation falls before 4 PM may make that the correct forecast. However, the latest NBM still shows higher median snow totals as shown earlier.
My GFS snow experimental forecast is much higher and may very well be wrong, especially if much precipitation falls before 4 PM. But here’s the latest in what I’m calling ‘experimental’ forecast based on GFS data —
My forecast above isn’t very different than the latest NBM median—
The real time weather analysis (RTMA) shows low pressure just beginning to form off the coast, as picked up by 3 hour barometric change—
Final thought for tonight. Snow during this period in February melts quickly. Sun angle is high and even with clouds, radiant insolation is strong. It’s not expected to be frigid afterwards like after the last storm.
Sunday Snowstorm Update
Posted Saturday 02/21/26 @ 4:46 PM — Let me address a few things that were not given attention to.
Current water vapor shows the storm beginning to form near SC coast—
Precipitation starts as either light rain or light snow or a mix as early as 5 AM Sunday near the city.
- Despite falling as snow by 1-3 PM, little accumulation occurs until 4 PM
- Winds pick up about the same time. Winds 20 mph gusting to 40 mph.
- Precipitation ends around 12-1 PM Monday, later somewhat in eastern NJ.
The latest NBM (19z) median snow totals are below. The mean totals are much higher. I’m still leaning towards these values.
Where could these totals go wrong? The RRFS has a good portion of the precipitation falling during Sunday but not accumulating. Is it a model error or does it know something the other models don’t? Here’s the RRFS time line—
I’ll update this evening if things change.
Yet Another Storm Update
Posted Saturday 02/21/26 @ 11:41 AM — The latest GFS just became available. Here’s its built-in snow depth parameter (which I find to underestimate snow accumulations)—
Here’s what I’m calling my “experimental” snow accumulation estimate, using my own algorithm calculations on GFS data—
Updates later this afternoon. Check back.
Winter Storm Update
Posted Saturday 02/21/26 @ 10:17 AM — Additional models have become available. A picture is worth a thousand words—
Timing update: Light rain and or snow begins as early as 4 AM Sunday. By 9 AM, the latest RRFS shows this precipitation type:
Precipitation falling as snow does not equate to accumulating snow. Temperatures above freezing with high sun angle and insolation through clouds in late February will likely reduce or eliminate snow accumulation before late afternoon or evening in many areas.
Updates later. Stay tuned.
Winter Storm Update
Posted Saturday 02/21/26 @ 9:24 AM — The models still show some differences in snow totals. What had looked like a uniform move to the higher end last night has splintered again into the lower totaling ECMWF/ECMWF-AI and the NOAA models GFS/NAM/HRRR which are forecasting higher amounts. (For reasons to be determined, the new still unreleased RRFS is in the low end of about 5-7″.) The latest NAM, NBM and others will be available over the next hour or two.
Much, but not all of the storm, now falls into the range of the high resolution HRRR.
The latest HRRR (whose forecasts only extend to 48 hours) includes a part of the storm up to 7AM Monday—
I’ll be making additional updates before noon. Stay tuned.
Storm Update
Posted Friday 02/20/26 @ 10:15 PM — A quick update. Tonight’s models have moved towards higher snow totals. The NBM median is almost as high as the mean.
The latest NAM is even higher. Updates Saturday morning.
https://www.meteor.iastate.edu/~ckarsten/bufkit/image_loader.phtml?site=kphl
Experimental
Posted Friday 02/20/26 @ 5:51 PM — With the soon to be retired NAM, I’ve been working on a snow algorithm with considerable help from Anthropic’s Claude AI that uses my snow forecasting technique derived from the old NAM FOUS data that served me so well years ago. I’ve applied it to the GFS model data. Probably not ready for prime time, but here’s the latest GFS model snow accumulation forecast based on this very experimental algorithm—
Major Snowstorm Increasingly Likely
Posted Friday 02/20/26 @ 5:18 PM —The models have come and they are all moving towards a major snowstorm for the Delaware Valley and NJ late Sunday into Monday. Details about the timing are below.
First, as described earlier, I’ve resurrected my favorite model for snowstorms in Philadelphia. This will likely be its last snow forecast for our region, since the model will be retired sometime this year when the RRFS becomes operational. Here’s the NAM snow forecast—
I’ll get more into the details as the weekend progresses, but I’m going to cut to the chase and post the latest Model Blend Mean and Median foreasts—
Here’s the NBM median forecast. I’ve been leaning towards the median forecast, but I think it may be too low. Somewhere between the median and mean sounds about right.
My regular Weekend Weather Forecast is below:
Major Snowstorm Increasingly Likely
Originally Posted Fri 4:55 PM — This weekend’s weather will start tranquil and will likely end much less so.
Here’s the setup as shown in current water vapor imagery—
Saturday Forecast
Clouds early morning then breaking for sun late morning. Cloudiness returns early afternoon in most areas except southern Chester/Delaware counties. Breezy winds 8-16 mph will make temperatures feel closer to 40º.
NBM high temperatures: Blue Bell, PA 47º Philadelphia, PA 49º
Higher than Average Uncertainty (based on standard deviation): ± 2.4º
Sunday Forecast
Major Snow Storm Likely for our Region
Light precipitation moves in during the morning hours. A mix of snow and rain possible and and where it snows, there will be little accumulation until evening. It will snow despite ground temperatures above freezing because just 1500 feet above ground, temperatures fall off rapidly below freezing.
Near ground temperatures drop towards evening as the storm picks up in intensity. Strong winds and heavy snow likely. Updates through the weekend. Snow tapers off late Monday morning.
NBM high temperatures: Blue Bell, PA 34º Philadelphia, PA 41º
Average Uncertainty (based on standard deviation): ± 1.4º
